Investigations on the thermo-chemical stability and electrical conductivity of K-doped Ba3 − xKxCaNb2O9 − δ (x = 0.5, 0.75, 1, 1.25)

In this paper, we report the synthesis, crystal structure and electrical transport properties of new K-doped Ba3CaNb2O9 (BCN) and investigate their chemical stability in H2O and pure CO2 at elevated temperature. The powder X-ray diffraction (PXRD) of Ba2.5K0.5CaNb2O9 − δ, Ba2.25K0.75CaNb2O9 − δ, Ba2KCaNb2O9 − δ, and Ba1.75K1.25CaNb2O9 − δ showed the formation of a single-phase double perovskite (A3BB/2O9)-like cell with a lattice constant of a ∼ 2ap (where ap is a simple perovskite cell of ∼ 4 Å). Perovskite-like structure was found to be retained after treating with CO2 at 700 °C and also after boiling H2O for 120 h. The lattice constant of CO2 and H2O treated samples was found to be comparable to that of the corresponding as-prepared compound. The total electrical conductivity of all the investigated K-doped BCN increases with increasing K content in BCN in various atmospheres, including air, dry H2, wet N2 and wet H2. The electrical conductivity in dry and wet H2 atmospheres was found to be higher than that of air in the temperature range of 300-700 °C, while in wet N2 a slightly lower value was observed. Among the compounds investigated in the present study Ba1.75K1.25CaNb2O9 − δ showed the highest total electrical conductivity of 1 × 10− 3 S/cm in dry H2 at 700 °C with an activation energy of 1.28 eV in the temperature range of 300-700 °C.